1. Technical Field
The present disclosure relates to an organic light emitting diode display device, and more particularly, to an organic light emitting diode display device where degradation in display quality due to a color-mixed emitting layer through a soluble process is prevented and a high resolution is obtained.
2. Discussion of the Related Art
Recently, various flat panel displays (FPDs) such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, organic light emitting diode (OLED) display devices and field emission display (FED) devices have been widely researched and used.
Among various FPDs, since the OLED display device of an emissive device does not require an additional light source such as a backlight unit for the LCD device, the OLED display device has a light weight and a thin profile. As compared with the LCD device, the OLED display device has superior properties in a viewing angle, a contrast ratio and a power consumption. The OLED display device is driven by a direct current (DC) low voltage and has a high response speed. Since an internal element of the OLED display device is a solid, the OLED display device is resistive to an external impact and has a wide available temperature range. Specifically, since a fabrication process for the OLED display device is simple, a production cost for the OLED display device is reduced as compared with the LCD device.
FIG. 1 is a plan view showing a pixel of an organic light emitting diode display device according to a related art.
In FIG. 1, a pixel 10 of an organic light emitting diode (OLED) display device according to the related art includes first to third sub-pixels 11a to 11c sequentially arranged along a row direction. The first to third sub-pixels 11a to 11c display red, green and blue colors, respectively, and constitute a pixel. The pixel is divided into the first to third sub-pixels 11a to 11c by a bank layer 73.
FIGS. 2A and 2B are cross-sectional views, which are taken along a line II-II of FIG. 1, illustrating a process of laminating an emitting layer in each sub-pixel.
In FIG. 2A, a bank layer 73 is formed on a substrate 11. The bank layer 73 includes openings to divide first to third sub-pixels 11a to 11c (of FIG. 1). A red emitting material solution 12a is dropped in the opening of the bank layer 73 corresponding to the first sub-pixel 11a, and a green emitting material solution 12b is dropped in the opening of the bank layer 73 corresponding to the second sub-pixel 11b. Although not shown, a blue emitting material solution is dropped in the opening of the bank layer 73 corresponding to the third sub-pixel 11c. 
In FIG. 2B, a drying step is performed for the red emitting material solution 12a, the green emitting material solution 12b and the blue emitting material solution to form an emitting layer in the openings of the bank layer 73. The emitting layer includes a red emitting layer 13a displaying a red color, a green emitting layer 13b displaying a green color and a blue emitting layer (not shown) displaying a blue color, and the red, green and blue emitting layers 13a and 13b are disposed in the first to third sub-pixels 11a to 11c (of FIG. 1), respectively. The red emitting layer 13a is formed in the opening corresponding to the first sub-pixel 11a, the green emitting layer 13b is formed in the opening corresponding to the second sub-pixel 11b, and the blue emitting layer is formed in the opening corresponding to the third sub-pixel 11c. The red, green and blue emitting layers 13a and 13b are formed through a soluble process such as an inkjet printing method and a nozzle printing method.
Since the bank layer 73 confines the red, green and blue emitting material solutions 12a and 12b having a water solubility, the bank layer 73 may be formed of a hydrophobic material or a top surface of the bank layer 73 may have a hydrophobicity through a surface treatment.
A pile up phenomenon where edge portions of the red, green and blue emitting layers 13a and 13b are piled up on a sidewall of the bank layer 73 may occur during the drying step. As a result, uniformity in thickness of the red, green and blue emitting layers 13a and 13b is deteriorated in each of the first to third sub-pixels 11a to 11c. 
The bank layer 73 between the first to third sub-pixels 11a to 11c functions as a separator preventing a mixing of the red, green and blue emitting material solutions 12a and 12b. Accordingly, the bank layer 73 has a horizontal bank width BW equal to or greater than about 16 μm.
Further, for dropping the red emitting material solution 12a, the green emitting material solution and the blue emitting material solution in the opening of the bank layer 73 through a soluble process, each of the first to third sub-pixels 11a to 11c is required to have a width equal to or greater than a minimum dropping width.
Recently, an OLED display device having a high resolution has been widely researched. For obtaining the OLED display device of a high resolution, a number of pixels per unit area of a display region should increase and a bank width of a bank layer dividing sub-pixels should decrease. When the bank layer is formed to have the bank width smaller than about 16 μm for the OLED display device of a high resolution, the red, green and blue emitting material solutions 12a and 12b may be mixed during the dropping step, and a mixed emitting layers may be formed in each of the first to third sub-pixels 11a to 11c after the drying step. As a result, a display quality of the OLED display device may be reduced due to the mixed emitting layers.
Further, since each of the first to third sub-pixels 11a to 11c has a width equal to or greater than a minimum dropping width, reduction in a size of each sub-pixel is limited and increase in a number of pixels per unit area is limited.